Modified Disturbance Function Method for a 6-6 Gough–Stewart Parallel Manipulator to Traverse the Singularity Hypersurface

Due to the motion uncertainty at the singular point, while the manipulator traverses the singularity hypersurface and moves from one singularity-free region to another, its motion is uncertain. To obtain a desired motion after it traverses the singularity hypersurface, the disturbance function approach was presented by the authors. Because the configuration transformation process takes place within the maximum loss control domain (MLCD), the motion uncertainty within the MLCD still exists. In order to eliminate this kind of motion uncertainty, a modified disturbance function method is presented in this paper. With the aid of the optimization method, the modified disturbance function is constructed through setting up the constraint equations to ensure each trace point locating beyond the MLCD corresponding to the perturbed singular point, and permitting some components of the configuration parameters with a little deviation. Under the action of the modified disturbances, the manipulator moves beyond the MLCD and traverses the singularity hypersurface with a controllable motion.